Most companies outline sample collection procedures in a Best Practices write up. Consistency in sample collection and sample processing is the most important variable for good sample analysis.
Samples should be collected and immediately taken to the laboratory or packaged for shipment to an outside lab in a sealed moisture barrier container or bag. If sending samples to an outside lab an additional moisture barrier tape should be applied around container lid. If samples are delivered to an in-house lab the procedure must outline for lab personnel the time to grind or process sample prior to measurement.
Calibration samples should be done individually meaning that sample one is ground, weighed, placed in oven for specified time interval at specified temperature for that product and weighed again for moisture determination. At that point the next sample is processed. Grinding all samples initially introduces an opportunity for increased variation while they await analysis unless all samples can be placed in the same oven immediately.
Consistency is the key to this process. If the first shift collects samples and the lab analyzes these samples when received, results are good. If another shift or operator collects the samples in a different manner or lets them sit for a while before bringing to the lab, or the lab lets samples accumulate before processing, variations can occur. Consistency is important for successful calibration.
Alternatively, samples can be created in the lab and allowed to equilibrate. These samples can be used for calibration. A final double- blind target set point sample should be analyzed and averaged to determine any offset (zero) adjustment on-line.
Other parameters such as fat and oil are subject to stratification and a well-mixed double-blind sample analysis is even more important for these constituents during calibration.